Thousands reached for their mobile phones as power went off
The Danish capital, Copenhagen, and parts of Sweden have been hit by massive power cuts.
Around four million homes and businesses lost supplies at around 1240 local time (1040GMT). Engineers restored most power by late afternoon, but the exact cause of the cuts remained unclear.
The problem stretched as far north as the Swedish capital, Stockholm, where the underground railway reportedly shut down for half an hour.
The blackout follows similar incidents in London and in a huge swathe of North America in August.
Sabotage was not suspected, police said, but some residents said their first thoughts were of a possible terrorist connection.
"People were out everywhere and there was a sense of fear as to what this meant," said one emailer to BBC News Online.
"Blackouts happen in the winter, but this made us wonder, since we have seen New York and London this year."
Electricity officials said the power cuts started when a main transmission line connecting Sweden and Denmark was affected.
Reports said a storm which swept through the area, bringing down trees, may have been a factor, but electricity officials said it was impossible to confirm whether the timing was a coincidence.
At least two Swedish nuclear plants - Oskarshamn and Ringhals - appear to have then developed problems and had to shut down production units.
Two million consumers in southern Sweden and 1.8m in Copenhagen were affected.
Some people were trapped in trains in a tunnel linking the Danish islands of Funen and Seeland. Others were stuck in lifts for up to two hours.
The Danish island of Bornholm was also hit.
Copenhagen airport and the Oeresund bridge and tunnel, linking the capital to Sweden, were reportedly closed, with scenes of traffic chaos in Copenhagen centre.
Railway and underground train services ground to a halt. Officials said passengers on at least two new driverless underground trains were evacuated without incident.
Reporters said hundreds of people emerged from shops in Copenhagen city centre to see what was happening, and used their mobile phones to contact their families.
Hospitals switched to be using emergency generators.
Nuclear power officials insisted that there was no safety threat from the shutdowns, which happened if there were big imbalances in the network and pressure suddenly fell.
"The security systems there worked just as they
should," said Anders Jorle, chief spokesman at the Swedish Nuclear
We asked you for your power cut experiences and views. Here is a selection of your replies.
Something's afoot methinks. What's with all these blackouts? Anyway, the Danes are pretty cool and take things like this in their stride. I'm sure the capital will be operating at its usual efficiency after a few hours. Very, very strange though...
Julian Howkins, Denmark
The third major power outage in two months... the two other ones happened in countries where government supported the war too. Time will tell if there is a link between all theses blackouts. Hopefully it is just bad luck...
If Europe is more closely interconnected, as is intended, could a simple incident in a small area lead to the collapse of each interconnected region like a domino effect? Is this because the spinning reserve capacity of the regions affected are insufficient to take up the shortfall in available power?
Gordon Gosling, England
The Danish power cuts have affected Greenland as well. The Bank of Greenland announced that the power cuts had affected all transactions between Greenland and Denmark, leaving Greenlanders with no oportunity to shop.
Edward Moerch, Greenland
I got stuck in a lift for an hour. There were seven of us - five women and two men. The women were really terrified. When power was restored a few minutes ago, there was hugging and kisses as soon as we got out of the lift.
John Birongo, central Copenhagen
I went down to the city centre where almost all the shops, government agencies, coffee houses, street lights, had a blackout. People were out everywhere and there was a sense of fear as to what this meant. I have not seen something like this in my 14 years in this country. Blackouts happen in the winter, but only up in northern Sweden, due to the snow. But this made us wonder, since we have seen New York and London this year.
I was awakened by the sound of four cars crashing into each other outside my window because of the non-working traffic lights. People were stuck in the elevators of my building for almost two hours. I guess this shows how dependent we are on certain things and how vulnerable our society is.
Henrik S., Sweden
I work in a helpdesk serving the Scandinavian countries, and of course, the power cut resulted an influx of phone calls from users, when they couldn't connect to Copenhagen, where the regional headquarters of our company are located. Many feared a terrorist attack and were really afraid.
Mika Torvinen, Belgium
I live in Norrköping, far north from this area, and, still the power was down here for some hours. We had experts in the media warning after the much bigger blackout in northern USA, that this could happen in Sweden too. If it can happen this easily just because of an accident like this, then we must be even more vulnerable to an intended sabotage.
When the phones went dead (ours lasted for one hour on the emergency battery pack) I got things done in the office that would otherwise have got lower priority. Let's have a one-hour power cut every day, just to do other things that get disrupted by phones and the constant blip announcing a new incoming email.
Thomas Bjorn Larsen,
I was trapped in the capital with very few ways of getting home. I managed to hitch-hike a lift home, but still it took more than two hours for a 30-minute journey. I saw the traffic chaos that streched for many miles outside Copenhagen, and and witnessed a motorway accident.
Jesper Edelmann Colmorten, Denmark
Just a short while ago when north-eastern America was hit by massive power shortages, Danish electricity supplier NESA publicly stated on national TV such a thing would never be able to happen in Denmark - in fact lights would not even blink if one power supply went out, it was said. They were right... for more than three hours no lights have blinked and the power is still gone.
Unexpectedly ISPs and mobile phone companies did not have sufficient backup power to last even 30 minutes. Compared to the four-hour power cut last year in Jutland, the effects are far worse this time. Maybe a sign of different levels of disaster preparation.
Traffic stood still in Malmo, otherwise a nice long coffeebreak.
I think it is unbelievable that such a modern country can have such terrible emergency systems. The phone system in Sweden began to crash almost immediately the power went down. It is clear that a country such as Sweden with little chance of natural disaster such as earthquakes is completely unprepared for such a problem as cut power. I am just glad it is still summer and not 20 degrees below. Was there no testing of the system for back up prior to 2000 like most Western countries?
I just think that all the power cuts that happened in the major cities, New York, London and now this are somehow related. I definitely think there is some sabotage involved even though officials deny it.
All rather bizzare really. In winter maybe, but a beautiful sunny autumn day? Everything just went dead - lights, phones, PCs.
For all the things that have gone wrong, I am still amazed at how well people handled themselves. Traffic was flowing nicely, the buses were running and people were very nice about making room for one another. But information has been horrible. No-one knew what was going on, many people were without cell-phone coverage and the like.
David Warmind, Denmark
I am sitting in my home in Denmark and the only link I have to information is through the internet - connected through a dial-up modem and with my notebook going on battery. Outside my window the traffic is chaos, the shops are closed, but every one is talking the situation with a smile - so far!
Nearly 10,000 delegates at a major cancer conference were left in the dark, their sessions interrupted, their PowerPoint presentations rendered useless, and journalists unable to file their copy from the conference as everyone twiddled their thumbs for an hour-and-a-half until power was restored.
Emma Mason, UK , working in Copenhagen
Now we have electricity back in Blekinge, Sweden, but only a few hours without and everyone is lost. Shops and banks and almost everything was closed for a while but life goes on. People should not be so dependent on electricity but we are...
I just stepped out of the underground metro, when everything suddenly blacked out. The local trains were also affected. I have never experienced a power-cut in Denmark before - it makes you wonder how dependent on electricity we all are. Many Danish internet sites are still not up and running.
We thought it was just our building and went into town to buy a pizza. The pizza baker explained the situation. So we went to get a sandwich instead. The sandwich place was indeed open (candle lights), but we couldn't pay. Neither of us had cash and the online credit card system didn't work. Interesting how dependent we are on electricity.
Kai Müller, central Copenhagen, Denmark
After Swedes realised there was no way to get over the bridge, they decided to go for a beer. At the cafe strangers were chatting with each other, and I heard one of them saying: "I imagine it was like this during the Second World War." Back at the office we drank yet another outage beer, and now, as the power has returned, my concentration is ruined.
I was sitting eating lunch in Elsinore, when suddenly all the power went down the drain. The traffic lights didn't work, so the streets were pure anarchy.
Funny to see how people react when things like this happens. They get all exited when everything is out of control. Maybe because we live in a very controlled enviorment.
What are the odds that this series of blackouts is perpetrated by a terrorist organisation testing their ability to exploit ageing electricity networks before launching one massive, synchronised attack supported by a comprehensive series of power cuts across the western world? I mean, we were told the London power cut was caused by a "fault" but that means diddly squat - they important thing is what caused the fault...
I was in the subway when the power failure happened. Everyone was terrified because it rarely happen here in Stockholm. We had to wait for a couple of minutes in the dark before the back-up lights got activated.
Pippi Langstrump, Sweden
Good luck everybody! I had a nice long walk home (five hours to be exact) when the power went out here in New York CIty. What I found was that people in New York really calmed down, pitched in, and helped each other out in ways that reminded me of the spirit of togetherness we felt after September 11th happened. I hope that things go as smoothly in your part of the world.
Mark Ellis, USA